The present invention relates to a semiconductor device, and more particularly to a semiconductor device that outputs a differential signal with the aid of an H-bridge circuit.
In a high-speed interface, there has been used a CML (current mode logic) signal that conducts a high-speed signal transmission by preventing an output transistor from being saturated by limiting an output current. However, there arises such a problem that because a signal level is set according to a current, a driver circuit that deals with the CML signal increases power consumption. Under the circumstances, in recent years, a VML (voltage mode logic) signal is frequently used instead of the CML signal. Because the VML signal is transmitted according to a voltage level, there is advantageous in that the power consumption of the driver circuit can be reduced more than the driver circuit that deals with the CML signal.
In the driver circuit that deals with the VML signal, an H-bridge circuit is used in order to balance the differential signal. Also, because the VML signal is attenuated in a transmission line, the VML signal is subjected to emphasis processing in order to compensate the attenuation of the VML signal.
Examples of the driver circuit that thus generates the VML signal with the aid of the H-bridge circuit are disclosed in Japanese Patent Unexamined Application Publication Nos. 2004-350273, 2009-49600, and 2010-56620. Each of Japanese Patent Unexamined Application Publication Nos. 2004-350273, 2009-49600, and 2010-56620 discloses the H-bridge circuit in which an internal resistor is coupled between first and second output terminals. Also, in each of Japanese Patent Unexamined Application Publication Nos. 2004-350273, 2009-49600, and 2010-56620, the differential signal is output with the aid of an emphasis mode for increasing an amplitude of the differential signal to be output, and a de-emphasis mode for decreasing the amplitude of the differential signal. In Japanese Patent Unexamined Application Publication No. 2004-350273, an output impedance of a driver that sets an output current is variable between the emphasis mode and the de-emphasis mode to make the amplitude of the differential signal variable. Also, in Japanese Patent Unexamined Application Publication Nos. 2009-49600 and 2010-56620, an internal resistance coupled between the first and second output terminals is enabled in the emphasis mode, and the internal resistance is disabled in the non-emphasis mode to make the amplitude of the differential signal variable.